1. Field of the Invention
The present invention relates to a transflective liquid crystal display (LCD), and more particularly, to a method for fabricating a transflective liquid crystal display using a silicon layer as transparent electrode of the transmissive region.
2. Description of the Related Art
Conventional transmissive type liquid crystal displays, comprise a backlight, suffer low image contrast when the environment is bright. That is, the color reproducibility is lower and the display is not sufficiently recognizable because the ambient light is brighter than a backlight of the display. Moreover, use of the backlight increases power consumption. Conversely, reflective type liquid crystal displays comprise a reflector formed on one of a pair of substrates rather than a backlight so that ambient light is reflected from the surface of the reflector. The method is disadvantageous, however, in that the display is less visible when the surrounding environment is dark.
In order to overcome the aforementioned problems, a display which realizes both a transmissive mode and a reflective mode in one liquid crystal display device has been disclosed in, for example, U.S. Pat. No. 6,195,140, the entirety of which is hereby incorporated by reference. Such a liquid crystal display device employs indium tin oxide (ITO) to serve as a transparent electrode and an upper electrode of a capacitor. FIG. 1A is a cross section of a conventional transflective liquid crystal display. FIG. 1B is the schematic arrangement of the transparent electrode and the reflective electrode of a conventional transflective liquid crystal display, wherein FIG. 1A is a cross section of the transflective liquid crystal display 10 taken along line I-I″ of FIG. 1B.
Conventional transflective liquid crystal displays, such as transflective thin film transistor liquid crystal displays (TFT-LCDs) comprise a bottom gate thin film transistor and a transparent electrode made of indium tin oxide (ITO). The fabrication processes are complicated and require excessive lithography steps and thus result in increased cost and lower production yield.
Referring to FIG. 1A, a transflective TFT-LCD device 10 comprises a lower substrate 12, an upper substrate 14, and a liquid crystal layer 16, wherein the lower substrate 12 serves as an active matrix substrate 12 and the upper substrate 14 serves as a color filter substrate 14 having a common electrode on its inner side. In FIG. 1B, a plurality of pixel areas are formed on the active matrix substrate 12. The pixel areas are defined by transverse scan lines 18 and longitudinal data lines 20. Each pixel area comprises a thin film transistor 20, a capacitor 30, a transmissive region T, and a reflective region R.
A first metal layer is formed on the lower substrate 12. The first metal layer is lithographically etched so as to define scan lines 18, a storage capacitor electrode 18a and a gate electrode 18b. A gate insulating layer 19 is formed on the lower substrate 12 covering the patterned first metal layer. A TFT island structure comprising a silicon layer 21, a channel protective layer 22, a source electrode 23a, and a drain electrode 23b is formed. A first ITO layer 24 and a second metal layer 25 are sequentially deposited and patterned into a predetermined shape to form the data lines 26. A portion of the first ITO 24a covers the storage capacitor electrode 18a to serve as a top electrode of the capacitor. One end of the first ITO layer 24a and the second metal layer 25b is formed on the source electrode 23b to serve as connecting electrodes 28. An insulating layer 29 having a contact hole 33 is formed on the resultant substrate 12. A second ITO layer 32 and a third metal layer 34 are subsequently deposited and patterned on the insulating layer 29. The second ITO layer 32 and the third metal layer 34 in the pixel area serve as pixel electrode P, wherein the overlap of the second ITO layer 32 and the third metal layer 34 forms a reflective region R, and the second ITO layer 32 not covered by the third metal layer 34 forms a transmissive region T. Moreover, the pixel electrode P is electrically connected to the respective capacitor 30 via the contact holes 33, while the capacitor 30 is electrically connected to the source electrode 23b via the connecting electrode 28.
The aforementioned electrode structure, however, is disadvantageous in that the capacitor 30 and the pixel electrode P are formed in different lithographical steps. As a result, more masks and lithographical steps are needed to define the first ITO layer 24 and the second ITO layers 32 leading to higher production cost and lower yield.
U.S. Pat. No. 6,331,100, the entirety of which is hereby incorporated by reference, describes another conventional transflective LCD device. A reflective electrode is directly formed on the lower substrate. A color filter and a transparent electrode are subsequently formed on the resultant substrate. By providing the reflective electrode with apertures, the area of the reflective region and transmissive region can be adjusted. FIG. 2 shows a cross section of another conventional transflective LCD device.
In FIG. 2, a transflective LCD device 40 comprises a lower substrate 42, an upper substrate 44, and a liquid crystal layer 46. An opaque metal layer 48, a color filter 50 and a transparent metal layer 52 are sequentially formed on the inner side of the lower substrate 42. A common electrode 54 is formed on the inner side of the upper substrate 44. The opaque metal layer 48 includes a plurality of apertures 49. The overlap of the opaque metal layer 48 and a transparent metal layer 52 forms a reflective region, and the transparent metal layer 52 not covered by the opaque metal layer 48 forms a transmissive region. The described related art still requires an ITO layer to serve as a transparent electrode. Therefore, an extra lithograpgy step is still required to pattern the ITO layer.